The present invention relates to combined optical systems in which an afocal variator optical system is specifically positioned to provide not only focusing means, but virtually constant magnification during focal translation.
Optical variators are typically used in optical systems to change the magnification of an image. For example, afocal variators have been used in projector lenses to alter the size of a projected image on a screen. In many instances, optical variator devices are used in combination with a front optical system or a rear optical system. In some instances they have even been used in combination with both a front objective system and a rear optical system. However, traditional optical systems which incorporate variator optical systems to alter the size of an image are not able to focus the image, and are usually only functional at relatively short back focal distances.
In the past where it has been desired to alter focal length, this has usually been accomplished by continuously or discretely changing the length of the optical system, or by changing the location or type of imaging lenses in the front or rear optical systems of the device, or in both front and rear optical systems. Hillman (U.S. Pat. No. 2,937,570) discloses a telescope system in which the image forming lenses are moved in order to focus the system. That is, focusing is accomplished by moving objective lens and focusing lens, which are part of the telescope's “formula-specific” objective imaging system. Focusing is not accomplished or taught to be feasible by moving a portion of an afocal variator, nor by moving a portion of any other non-image forming modular optical lens system. It does not include a central afocal variator module which does not comprise a portion of the image-forming optics. If any of the movable lenses of any of the systems taught by Hillman were removed, the entire system would be affected, very probably to the point that the system would no longer function for its intended purpose. Quenderff (French Patent No. 2,572,545) uses a zoom lens to make enlarged pictures, and also teaches the use of various art known mechanical devices for connecting together optical modules. However, it neither teaches nor suggests the use of a central afocal variator module as a focusing element.
Margolis (U.S. Pat. No. 4,988,173), in contrast, teaches the use of an afocal variator optical system which can be used in optical instruments, such as long-distance microscopes, as the mechanism for providing focus. However in this reference and all other references known to the applicant, no optical focusing systems have been used with an afocal variator which imparts virtually constant magnification through the range of focal translation. While the noted reference teaches the use of an afocal variator as the focusing means of optical systems, it does not additionally teach that under specific conditions and positions the afocal variator can, in and of itself, be positioned to impart virtually constant magnification through the range of focal translation.